1. Field of the Invention
The present invention relates to a method and apparatus for charging a gas into a bag and more particularly to a method and apparatus for charging a gas into a gas compartment provided in a sealed side edge portion of a bag.
2. Description of the Related Art
Japanese Patent No. 4,771,785 describes a method for charging a gas compartment portion of a bag with a gas in which a gas compartment of the gas compartment portion is formed integrally therewith and spaced away from the contents storing portion that stores contents for the bag.
More specifically, in this Japanese Patent No. 4,771,785, an incision or an opening used for placing the exterior of the bag in communication with the interior of the gas compartment portion is formed in the surface of the film that makes the gas compartment portion. The discharge outlet of a nozzle connected to a pressurized gas supply source is aligned with the incision or opening, with the back side of the bag being supported by a bag backing member, and gas is injected from the nozzle into the gas compartment portion of the bag through the incision or opening. While the injection is in progress, a blockage region configured in the vicinity of the incision or opening is held from both sides of the bag by a gas blocking gripper so as to block the fluid communication of gas between the incision or opening and the interior of the gas compartment portion. Then, the bag is sealed using hot plates contacted on both sides of the bag in the location of the incision or opening while the blocked state of the blockage portion is being maintained, thus sealing the incision or opening and entrapping the gas in the gas compartment portion.
In this Japanese Patent No. 4,771,785, the gas compartment portion is formed, for example, between the film sheets constituting the front and rear surfaces in the sealed side edge portion of the bag, or alternatively, if the film constituting the front and rear surfaces of the bag is a laminated film, the gas compartment portion is formed inside the laminated film at least on one side. Such a gas compartment portion can be formed not only in lay-flat bags, but also in bottom-gusseted self-supporting bags, as well as in bags provided with spouts.
If the gas compartment portion extends downwardly from the vicinity of the upper edge of the bag and the incision or opening is formed in the vicinity of the upper edge of the gas compartment portion, the gas compartment can be charged with gas by gripping, while the injection is in progress, a location below the incision or opening with a gas blocking gripper so as to block the fluid communication of gas between the incision or opening and the interior of the gas compartment portion and then completely sealing the mouth of the bag from both sides together with the incision or opening at the same time.
In Japanese Patent No. 4,771,785, the charging of the gas compartment portion with a gas can be accomplished as part of the bag packaging process (including lay-flat bags, gusseted bags, etc.).
More specifically, the bag equipped with a gas compartment is continuously or intermittently conveyed while being suspended with its two lateral edges held by grippers, and, while the bag is being conveyed, various packaging steps, including opening the mouth of the bag, filling it with the material to be packaged, sealing the mouth of the bag, etc., are consecutively carried out; and in these steps, the step of charging the gas compartment portion with a gas is carried out after the contents filling step. In this Japanese Patent No. 4,771,785, the charging of the gas compartment portion with a gas can be accomplished as part of the bag packaging process. Specifically, a bag provided with a spout is continuously or intermittently conveyed with its spout held by a bifurcate spout-holding member inserted between the top and bottom flanges formed in the spout and, while it is being conveyed, various packaging steps, including sealing the spout and the film in the mouth of the bag, sealing the two film sheets together in the mouth of the bag, filling the bag with the material to be contained therein, capping the orifice of the spout, etc., are carried out in a consecutive manner; and in these steps, the step of charging the gas compartment portion with a gas is carried out before the filling step. In either case described above, it is desirable that the sealing of the bag mouth be carried out simultaneously with the sealing of the incision or opening.
On the other hand, according to the description of Japanese Patent No. 5,104,073, an incision or an opening is made at the upper edge of a gas compartment portion formed in a sealed side edge portion of a bag, and a gas charging pathway is formed so as to extend from the incision or opening with a width thereof being narrower (smaller) than the other (or main) part of the gas compartment portion; and gas is injected through the incision or opening into the gas compartment portion, and while the injection is in progress, a location in the vicinity of (directly underneath) the incision or opening within the gas charging pathway is heat sealed, thus sealing the gas in the gas compartment portion. In the gas charging method of Japanese Patent No. 5,104,073, the step of injecting gas into the gas compartment portion and the heat sealing step are not be able to be separated; accordingly, when this method is used in, for example, an intermittently rotating rotary-type packaging apparatus, it is difficult to increase productivity in comparison with the gas charging method of Japanese Patent No. 4,771,785.
In the gas charging method described in Japanese Patent No. 4,771,785, the gas compartment portion expanded by a gas (air) is gripped by a gas blocking gripper while the gas injection into the gas compartment portion is in progress, so that the fluid communication of gas between the incision or opening and the interior of the gas compartment portion is blocked. At such time, the front and rear film sheets or laminated film of the gas compartment portion (blockage region) being gripped often do not collapse into a flat configuration; as a result, a gap is created in the gas compartment portion, thus making it impossible to completely block the fluid communication of gas between the incision or opening and the interior of the gas compartment portion. In such a case, a problem of leakage of gas from the gas compartment portion would occur after the nozzle and the bag backing member are retracted from the location of the incision or opening and before such a location of the incision or opening or a location nearby is clamped between hot plates and sealed.
This problem will be described with reference to FIGS. 22(a) through 23(b).
In FIG. 22(a), the reference numeral 1 designates a sealed side edge portion provided in a bag equipped with a gas compartment (see FIG. 1 in Japanese Patent No. 4,771,785), 2 designates a gas compartment portion formed vertically between the film sheets 3, 4 that constitute the front and rear surfaces of the sealed portion 1, 5, 5 designate gas blocking grippers, 6 designates a nozzle used for gas injection, and 7 designates a bag backing member.
The bag equipped with gas compartment illustrated in FIG. 22(a) corresponds to the bag equipped with gas compartment “1” described in Japanese Patent No. 4,771,785, and the gas compartment portion 2 corresponds to the gas compartment portion “5” (see in FIG. 1 of Japanese Patent No. 4,771,785 for both “1” and “5”), while the gas blocking gripper 5, nozzle 6, and bag backing member 7 correspond to the sub-gripper “7”, nozzle “11”, and bag backing member “12”, respectively, of this art (see FIGS. 2-4 of Japanese Patent No. 4,771,785 for these members). The bag equipped with gas compartment illustrated in FIG. 22(a) has two of its lateral edges gripped by bag-conveying grippers (corresponding to the grippers “8” in Japanese Patent No. 4,771,785), which are not shown in the embodiment of FIG. 4 of this art.
FIG. 22(b) shows a state in which the nozzle 6 and the receiving member 7 have advanced from the retracted positions illustrated in FIG. 22(a), the distal end (discharge outlet) of the nozzle 6 has been aligned with the incision or opening formed in the gas compartment portion 2, the bag backing member 7, which faces the nozzle 6, supports the back of the gas compartment portion 2, and a gas is injected into the gas compartment portion 2. The gas compartment portion 2 can be freely expanded in response to the pressure of the gas, and as a result of which the edge 1a of the side edge portion 1 of the bag is pulled in, thus moving a distance D towards the center of the bag equipped with gas compartment.
FIG. 23(a) shows that gas injection through the nozzle 6 is in progress while the gripping elements of the gas blocking gripper 5 has advanced from the retracted positions illustrated in FIG. 22(a) to grip both sides of a predetermined location of the bag equipped with gas compartment underneath the incision or opening formed at the upper edge of the gas compartment portion 2 (blockage region). During the process that the expanded gas compartment portion 2 is collapsed into a flat configuration, excess film 3, 4 expands sideways in the width direction of the gas compartment portion 2, and as a result, longitudinal creases 8 are produced on the opposite sides of the gas compartment portion 2.
In FIG. 23(b), the gripping elements of the gas blocking gripper 5 is closest to each other and the gas compartment portion 2 has been collapsed. In the area of the longitudinal creases 8 shown in FIG. 23(a), the film of the gas compartment portion 2 is folded and superimposed on the sealed portion 1; as a result, the gas blocking grippers 5 cannot completely collapse the blockage region of the gas compartment portion 2 into a flat configuration, and an extremely narrow flat space 9 is created in such a region.
In addition, in the gas charging method described in Japanese Patent No. 4,771,785, the width of the sealed side edge portion, in which the gas compartment portion is formed, is made considerably wider in comparison with the width of the gas compartment portion; and in addition, a gripping margin used for a bag-conveying gripper is provided outside (width W shown in FIG. 22(a)) the gas compartment portion (see FIG. 4 of Japanese Patent No. 4,771,785). In certain cases, the width of the sealed side edge portion, in which the gas compartment portion is formed, cannot be made significantly wider than the width of the gas compartment portion. Accordingly, when using such a bag equipped with gas compartment, it is difficult to provide a gripping margin for a bag-conveying gripper outside the gas compartment portion, and thus the gas charging method described in Japanese Patent No. 4,771,785 cannot be applied.